Induction is a common form for wireless power. Non resonant induction systems like transformers use a primary coil to generate a magnetic field. A secondary coil is then placed in that magnetic field and a current is induced in the secondary coil. Induction, however, has the disadvantage that the receiver must be very close to the transmitter in order to inductively couple to it. At large distances induction wastes most of the energy in the resistive losses of the primary coil. Resonant inductive coupling improves energy transfer efficiency at larger distances by using two coils that are highly resonant at the same frequency. However, both non-resonant and resonant induction wireless power methods are non-directive and irradiate the space around them. This can be disadvantage in some situations since there are regulations that limit human exposure to alternating magnetic fields because of concern for biological impacts on the users. Also, since they use low frequencies (KHz to 7 MHz) they cannot be used for high speed communication.